The fielders mitt was something of a hybrid having the the flexibility of a glove coupled with the greater surface area of a mitt to catch a ball. This 1912 patent by Burt Rogers for Victor Sporting Goods encased a glove in a sheath of leather. The design is really a refinement of Joe Gunson's original 1885 invention.
This is the glove assembly with the felt padding overlayed
This is the empty leather sheath to fit over the glove
This is the finished product after sewing the two pieces together. Like the earlier 1911 Victor "pita Pocket" glove, the finger stalls of the glove are only attached at the fingertips to the edge of the sheath. This was done to keep the flexibility of a standard glove.
Not sure if these are Victor fielders mitts but they do have the same characteristic of a flat top as opposed to the oval top of other brands